Solid Oxide Fuel Cell Thermodynamic Study

Çankaya University Journal of Science and Engineering Volume 14, No. 2 (2017) 134-151 Solid Oxide Fuel Cell Thermodynamic Study Youcef Sahli1,2,*, Bariza Zitouni3, Hocine Ben-Moussa1 1Department of Mechanical Engineering, Faculty of Technology. University of Batna 2, Algeria. 2Unité de Recherche en Energies Renouvelables en Milieu Saharien, URERMS, Centre de Développement des Energies Renouvelables, CDER 01000, Adrar, Algérie, 3Department of Food Technology. Institute of Veterinary Sciences and Agricultural Sciences. University of Batna 1, Algeria. e-mail: /, , Abstract: The aim of this work is the solid oxide fuel cell (SOFC) thermodynamic study. Particular attention is given to the electric power optimization. The Nernst potential and the over-potentials that are due to the concentration polarization, activation polarization and to the Ohm polarization represent the fuel cell potential. A FORTRAN language program was developed locally for the cell model simulation. From the result analysis, it appears that the developed model allowed understanding the operating condition effects on both potential and power density values. The obtained results show that the cell potential and the power density are proportional to the operating temperature changes and to the oxygen concentration in the oxidant, by cons, they are inversely related to the supply pressure changes, fuel moisture and to the electrolyte thickness. Keywords: SOFC, power density, over-potential, thermodynamic. 1. Introduction Among the fuel cell types, solid electrolyte cell (SOFC) delivers a large electric power. It is considered as a promising technology for its great global performance and its operating ability by several fuels. The electrochemical behavior remains the main research focus for the fuel cell development. The complexity and the multitude of phenomena involved in the fuel cell operation make its experimental study difficult. Thus, researchers incite to develop numerical simulation programs in order to predict better the phenomena behavior that intervenes and minimizes the costly experimental experiences. In this context, several studies have been addressed previously. Yang et al. [1] have developed an electrochemical model for solid oxide fuel cells to a supported anode (SOFC-AS) to analyze and improve the cell design. The presented model takes into ISSN 2564 – 7954 © 2017 Çankaya University CUJSE 14, No. 2 (2017) 135 account three over-potential types: activation, Ohm and concentration. They showed that the activation and Ohm over-potentials are the main responsible cause for the tension loss. Al Zahrani et al. [2] have presented and used a model for predicting the conventional SOFC performance under various operating conditions and design for low operating temperatures. Verma et al. [3] have studied the possibility of supplying the solid oxide fuel cells with reformed fuels. This can be beneficial because they are cheap compared to pure hydrogen. A biomass fuel can be easily modeled as a reformed fuel because it can be converted into H2 and CO using the gasification or the bio-degradation. This produced composition is mainly made in a gas reformer situated before the cell. Saebea et al. [4] have performed a study to evaluate the theoretical performance of a single cell of an SOFC integrated with a steam reforming process using three different renewable fuels: ethanol, glycerol and biogas. They studied the main operating parameter effects on the hydrogen production. Tippawan et al. [5] have applied a thermodynamic concept to identify a reforming process suitable for an SOFC supplied with ethanol. Three different reforming technologies are considered, specifically, steam reforming, partial and direct oxidation reforming. They showed the effects of the main operating parameters on the distribution of reforming products, such as (H2, CO, CO2 and CH4) in order to identify the best process for reforming ethanol for SOFC applications. This study is a continuation of our previous ones [6-15]. In [6], the thermoelectric performance of an intermediate temperature SOFC has been presented by a one-dimensional model for the parallel direction to the gas flow using the finite volume method. The heat is generated by the Joule’s effect and the loss due to the internal chemical reaction. In the reference [11], the power density and the hydrogen consumption of a planar SOFC are studied according to input parameters; such as the operating temperature, the operating pressure, the flow rates and the mass fractions by a one-dimensional electro-dynamic model using the finite difference method. In the reference [7], the hydrogen and water distribution depending on the anode thickness in the SOFC heart has been realized by a two-dimensional model based on the finite difference method in the perpendicular plane to the reactive gas flow directions. Reference [8] shows a two-dimensional numerical study of the temperature fields in the perpendicular plane to the gas flow of a planar SOFC heart at a supported anode under the chemical reactions effect. The reference [9] represents a study of the location and determination of the maximum temperature values in all solid and porous parts (electrolyte, interconnectors, anode and cathode) of the planar SOFC at a supported anode or a supported electrolyte, in a perpendicular plane to the gas flow under the polarization effects: Ohmic, activation and concentration. Reference [10] shows an analysis of the heat production and distribution in all solid and porous 136 Y. Sahli et al. parts of the planar SOFC at a supported anode under the effect of various over-potentials (Ohmic, activation, concentration and chemical), in the perpendicular plane to the gas flow direction in order to describe the thermal behavior during the operation. The reference [12] represents a comparative study of the heat distribution depending on the gas supply temperature between two planar SOFC configuration types. The first has a supported anode and the second has a supported electrolyte for the cases with and without the total heat source (Ohmic, concentration, activation and chemical), in all solid and porous parts (electrolyte, interconnectors, anode and cathode) of the planar SOFC. In [13], the molar fractions effect of the fuel constitutive chemical species (CH4, H2O, CO, CO2 and H2) on the heat distribution is studied in a planar SOFC at the supported anode in a two-dimensional environment and perpendicular to the gas flow direction. Heat generation/absorption due to the direct internal reforming in all solid and porous parts of the cell are discussed. The reference [14] presents a study of the produced heat behavior by the direct internal reforming depending on the temperature and pressure of the supply fuel in all parts of the planar SOFC at a supported anode in the perpendicular plane to the gas flow. In the reference [15], a comparative study of the heat generation in the three geo (...truncated)